The aim of this study is to investigate the effects of naltrexone, alone and combined with nicotine patch, on responses of smokers to smoking cues after 10 hours of tobacco deprivation. Smokers who are not seeking treatment will be assigned to one of six conditions: They will receive either 50 mg of naltrexone or a placebo pill, and also will wear a nicotine patch that has 0, 21, or 42 mg of nicotine during the tobacco deprivation period. Both the day before the medication and deprivation and at the end of 10 hours of deprivation all will be exposed to lit cigarette cues in the laboratory. Effects of the medications will be assessed on withdrawal measures, urge to smoke, psychophysiological measures, and the topography of smoking three test cigarettes. Studies such as these can help to identify potential interventions for tobacco cessation or withdrawal, and thereby could result in less suffering and mortality.